variations in salinity were much greater than they are today. Modern day salinities are all within 0.5 psu of the global average salinity of 34.7 psu, whereas salinities during the last glacial maximum (LGM) ranged from 35.8 psu in the North Atlantic to 37.1 in the Southern Ocean. There are some notable differences in the hydrography at the LGM and present day. Today the North Atlantic Deep Water (NADW) is observed to be more saline than Antarctic Bottom Water (AABW), whereas at the last glacial maximum it was observed that the AABW was in fact more saline; a complete reversal. Today the NADW is more salty because of the Gulf Stream; this could thus indicate a reduction of flow through the Florida Straits due to lowered sea level. Another observation is that the Southern Ocean was vastly more salty at the LGM than today. This is particularly intriguing given the assumed importance of the Southern Ocean in oceanic dynamical regulation of ice ages. The extreme value of 37.1 psu is assumed to be a consequence of an increased degree of sea ice formation and export. This would account for the increased salinity, but would also account for the lack of oxygen isotopic fractionation; brine rejection without oxygen isotopic fractionation is thought to be highly characteristic of sea ice formation. The increased role of salinity The presence of waters near the freezing point alters the balance of the relative effects of contrasts in salinity and temperature on sea water density. This is described in the equation, where is the thermal expansion coefficient and is the haline contraction coefficient. In particular, the ratio is crucial. Using the observed temperatures and salinities, in the modern ocean, is about 10 whilst at the LGM it is estimated to have been closer to 25. The modern thermohaline circulation is thus more controlled by density contrasts due to thermal differences, whereas during the LGM the oceans were more than twice as sensitive to differences in salinity rather than temperature. In this way, the thermohaline circulation can be considered to have been less "thermo" and more "haline". See also Fresh water References External links History of salinity. Chemical oceanography Aquatic ecology Oceanography Coastal geography